The present invention relates generally to transmission controls, and more specifically to a direction control, a combination cruise and direction control, and a brake interlock system for a hydrostatic transmission.
Controls for an off-road vehicle having a hydrostatic transmission typically include a direction control lever, or direction control pedals, along with some form of transmission speed ratio control which may be a separate lever or pedal or which may be combined with the direction control devices. With many transmission systems, a foot pedal is utilized to select speed ratio and must be continuously held in the desired position during operation of the vehicle which can result in operator fatigue. Maintaining the transmission in the desired speed ratio becomes difficult over extended periods of operation. Although numerous controls have been available to maintain the speed ratio control in a preselected position, most of the controls have suffered from one or more disadvantages. A number of the speed ratio controls require an extra lever or the like which adds to the cost and complexity of the transmission system and which is not always easily understood or easily operated. Adjusting linkages during manufacture of the vehicle to assure proper direction and speed ratio control can be a difficult and time-consuming task with some control arrangements. In addition, many types of presently available controls do not afford easy incorporation of the various systems such as cruise control and park brake interlocks into a conveniently manufacturable and usable package.
It is therefore an object of the present invention to provide an improved transmission control that overcomes the above-mentioned problems. It is a further object to provide such a control which is simple and logical in operation. It is still another object to provide such a control wherein the speed ratio of the transmission may be selectively maintained in a preselected condition.
It is a further object of the invention to provide an improved transmission speed ratio and direction control. It is another object to provide such a control which is easy to adjust during manufacture and easy to operate, and which facilitates the design and interaction of other vehicle systems such as brake and cruise controls. It is still another object to provide a transmission speed ratio and direction control wherein speed ratio is selected by a single foot pedal and direction by a single lever.
It is still another object of the present invention to provide an improved transmission control having a speed ratio maintaining mechanism which requires fewer control levers or pedals than most previously available transmission controls. It is a further object to provide such a control which is substantially improved ergonomically over most previously available controls. It is still another object to provide such a control which is relatively inexpensive and simple in construction and is easy to adjust during set-up.
It is still a further object of the present invention to provide an improved transmission control which has relatively few parts, is low in cost, and provides positive, fail-safe operation. It is another object to provide such a control arrangement which includes an improved brake interlock system. It is still another object to provide such a control including a direction control lever and a speed ratio control foot pedal, wherein a cruise control function may be selected at any time the direction control lever is in the position which selects the forward mode of operation.
In accordance with the above objects, a direction control lever is mounted on the console at one side of an off-road vehicle, and a single foot-operated speed ratio selecting pedal is rockably connected to the floor of the vehicle. The direction control lever and speed ratio control pedal are connected through shuttle structure to the transmission control rod of a hydrostatic transmission. The direction control lever has a reverse position wherein, when the foot pedal is depressed, the shuttle structure moves the transmission control arm through a range of ratios to operate the vehicle in the reverse direction. Pushing the direction control forward to a detent moves the shuttle structure to cause the foot pedal to operate the transmission control arm through a range of forward speed control ratios. When the forward direction is selected by the control lever, the lever may be pushed forwardly past the detent to a cruise control position. In the cruise control position, a pawl pivotally supported by the lever engages a tooth portion on the shuttle structure to maintain the transmission in the forward speed control ratio selected by the foot pedal. The cruise control for maintaining the transmission in the desired forward speed control ratio may be disengaged by simply moving the control lever rearwardly from the cruise control position to the detented forward position, or by depressing the brake pedal which automatically moves the lever rearwardly from the cruise control position. Therefore, the transmission control structure combines the operation of direction control and cruise control to eliminate the need for an additional cruise control lever or the like. A very simple, logical combination of controls is provided that is easy to understand and operate, that requires few additional parts, and that is relatively low in cost. The desired transmission speed ratio may be easily selected by the foot pedal in either the forward or reverse modes of operation and maintained by the cruise control during forward mode operation. The structure provides positive, fail-safe operation, and the transmission control arm or swash plate cam can be easily adjusted during manufacture with the engine running by placing the control linkages in a dead-center neutral position. The control arrangement also includes an improved brake interlock system, the design of which is facilitated by the side-mounted direction control lever and includes structure for providing a dead-center neutral condition preventing operation of the speed ratio control.
These and other objects, features and advantages of the present invention will become apparent to those skilled in the art from the description which follows and from the drawings.